Protection of organic materials against oxidation



United States Patent Ofiiice 3,507,789 Patented Apr. 21, 1970 3,507,789 PROTECTION OF ORGANIC MATERIALS AGAINST OXIDATION Israel J. Heilweil and Albert L. Williams, Princeton, N.J.,

assignors to Mobil Oil Corporation, a corporation of New York No Drawing. Filed June 22, 1967, Ser. No. 647,947 Int. Cl. C10m 7/02, 7/30 US. Cl. 252-19 12 Claims ABSTRACT OF THE DISCLOSURE Metallic antioxidant agents in finely divided form are provided, and methods of preparing them, for protecting oxidation-sensitive materials against oxidation at high temperatures.

CROSS-REFERENCES TO RELATED APPLICATIONS Certain products of the method described and claimed in copending application Ser. No. 647,344, filed June 20, 1967, are of use in the present case as antioxidants.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION Significant antioxidation protection of organic materials at temperatures above 400 F. is obtainable by using an antioxidant agent in finely divided form, preferably in the form of colloidal metallic particles of a diameter in the range of 50 angstroms to 0.5 micron, the particles having an external surface comprising a metal of atomic number 46, 47, 50, 51, 82, and 83.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS The invention relates to the protection against oxidation of various organic materials that are sensitive to oxidation, such as lubricants, and particularly lubricants intended for high temperature service as in jet engines. A well known class of lubricants, or base stocks therefor, of this type comprise the polyphenyl ethers; others include esterlubes, comprising the reaction products of dibasic acids with alcohols, such as di-Z-ethylhexyl sebacate, or the reaction products of polyhydric alcohols with organic acids such as pentaerythritol tetrapelargonate. Fluorinated lubricants, greases, petroleum fractions, and the like are also capable of protection using the method described herein.

' Particularly suitable are lubricants which already possess some resistance to oxidation, such as those having inherent resistance like the polyphenyl ethers, or those containing a conventional antioxidant like the commercially available amine and phenol types. The latter agents are, by themselves, indequate at the higher temperatures contemplated herein, being thermally unstable or too volatile; however, they are useful to protect the lubricant at temperatures up to 400 or 450 F.

A preferred class of lubricants which may be protected according to the invention is that described and claimed in US. 3,247,111, which may be set forth briefly as comprising the following components:

(a) A major proportion of an ester formed by reaction of a pentaerythritol and an organic acid having from 2 to about 18 carbon atoms per molecule;

(b) From about 0.5 to about 5% by weight of an antioxidant of the chain stopper type, including amines, phenols, esters, phosphites, etc., based on the lubricant;

(0) About 0.0001 to about 1% by weight of an equimolecular salt of l-salicylalaminoguanidine and an aliphatic carboxylic acid having about 14 to about 18 carbons;

(d) About 0.001 to about 1% by weight of a polyhydroxyanthaquinone;

(e) About 1 to about 10% by weight of a phosphorous compound chosen from neutral organic phosphates and phosphites; and

(f) Preferably about 0.0001 to about 0.01% by weight of a defoamant which may be a conventional one or chosen from a lower alkyl silicone polymer. Specific examples of the foregoing components are set forth in the said patent.

Besides lubricants, higher molecular weight organic materials like plastics and polymers may be protected. These materials may encounter high temperatures during formulation, or fabrication or use, and their protection is desirable for obvious reasons.

The use of the described metallic particles in lubricants has been found to provide substantial antioxidant protection, resulting in a service life increase ranging from 10% up to 200%, or more, longer than that of a control comprising a like lubricant containing no metallic particles. Furthermore, the acidity of the protected lubricant tends to be reduced by a factor of up to 50%, or more, by comparison with the control; and there is better protection against viscosity change. As indicated, the useful metals are those of atomic numbers 46, 47, 50, 51, and 83, corre sponding to palladium, silver, tin, antimony, and bismuth. These are all fairly soft metals and thus are not likely to abrade the device being lubricated. Preferred hardnesses range from about 1.2 to about 3.3 Mohs scale. The metals are also non-corrosive, even to parts made of magnesium and copper. They are further characterized by being insoluble in the lubricant, and, under conditions of service, by being substantially non-reactive with oxygen, water, steam, and carboxylic acids. Furthermore they do not form soluble salts that are pro-oxidant. Another useful metal is lead, atomic number 82, which although reactive with oxygen under service conditions, leads to compounds soluble in the lubricant and thus non-abrasive. The preferred metals are tin and silver, especially tin.

The invention contemplates alloys of the foregoing metals, particularly tin alloys and silver alloys such as lead-tin-antimony type metal, lead-silver and lead-tin solders, silver-tin alloy, tin-antimony alloy known as Brittania metal, and the like.

As indicated, the size of the particles is generally in the range of 50 angstroms to about 0.5 micron, preferably 50 to 1000, and more preferably 50 to 200 angstroms. These fine sizes, which are in the colloid size range, provide a large surface area per unit weight, tend to favor the dispersal of the particles, and create an opportunity for high specific activity. When used with oils, the particles should be small enough to pass through the pores of oil filters, and as conventional filters have pore diameters of about 0.5 micron, or somewhat less, it will be seen that the described size ranges are quite adequate for this purpose.

In the case of tin, in order to make particles of the desired fine size, it is preferred to take a substrate of a material other than tin and to coat the same with tin. The substrate should be one available in the necessary fine size, and may be selected from such materials as copper, zinc, zinc oxide, thoria, carbon black, magnesia,

alumina, boron nitride, silicon carbide, silica, titania, and any other suitable material, including other oxides. Also, a metal like copper may be placed on a substrate like carbon black or titania, and then tin deposited on the copper; such a material is characterized by its ease of preparation. The foregoing techniques may be used in the case of silver to improve the dispersivity of the particles, and may also be employed for the other metals. As will be understood, the metal on the outer surface of these multi-component particles comprises the active antioxidant; it may range in thickness upwardly from that of a monolayer or even an incomplete mono-layer. Suitable procedures for depositing a metal on a substrate include the thermal decomposition of a compound of the metal in the presence of the substrate, thereby to deposit the metal on the latter; the reduction of a compound of the metal, using a reducing agent, in the presence of the substrate and a solvent for the compound, to form the elemental metal which then deposits on the substrate; the displacement of the metal from its solution by means of another metal above it in the EMF series in the presence of the substrate, using the technique of immersion deposition; and the electroless deposition of the metal on a substrate.

Where the metal particles comprise active metal alone, they may be formed in the desired fine sizes by the first, second, or third methods described in the preceding paragraph, except that a substrate is not present; and they may also be produced by reducing a metal compound in situ in the lubricant or other oxidation-sensitive material, thereby forming the metallic particles directly in the material. Fine metallic particles may also be made by vaporizing the metal by heat or an electric arc and then condensing the vapors. It will be understood that some metals are commercially available in the desired fine size.

The concentration of metallic particles in the lubricant in terms of active metal should be sufficient to provide an accepted slow rate of oxidation of lubricant; preferably it is of the order of 0.005 to 0.5% by weight, although concentrations as low as 0.003% (30 ppm.) have proved effective, and concentrations as high as 5.8% have been used with good results. Generally the concentration is in the range of 0.005 to 1.0% by weight, and this applies to other materials desired to be protected. For greases, plastics, and polymers, the concentrations may extend as high as or 20% by weight.

It should be pointed out that the metallic particles, by virute of their fine size, are suspendable in the lubricant; and they are substantially non-coagulating, being able to maintain themselves in a highly dispersed state. After they have served their purpose of protecting a material against oxidation, they are recoverable from it, as by means of centrifuging, in a substantially unchanged state; thus, they may be reused, if it is so desired.

In the case of greases, plastics, polymers, and the like, which are normally in a semi-solid or solid state, and which are not required to pass through filters, the antioxidant particles may be effectively used in larger sizes, i.e., above the colloid size range, although colloid sizes are preferred.

The particles are capable of very substantially increasing, i.e. doubling or tripling the useful lifetime of high temperature lubricants, as shown in Tables 1 and 2 below. In any event, an improvement of at least 10% in lubricant lifetime is generally obtainable. Coincidentally with this result is a reduction in acidity, by comparison with a control, and more often than not there is a smaller viscosity increase than with the control. These interesting results are obtainable without danger of corrosion to the parts being lubricated, even when such parts contain sensitive metals like magnesium and copper.

The invention may be illustrated by the following examples.

Example 1 Antioxidant particles were prepared each comprising a coating of tin on a copper substrate. For their preparation, 10 ml. of a suspension of copper powder in water was added to ml. water, heated to about 70 C., placed in a Waring Blendor and agitation started, and then there were added dropwise 200 ml. of a previously heated conventional tin plating solution known as Shipleys bt-27,

available from Shipley, Incorporated, Waltham, Mass.

The addition required 3 to 4 minutes, and agitation was continued for 2 more minutes. The resulting dispersion was mixed with 200 ml. acetone, filtered through a silver membrane having openings of 0.25 micron, washed with 2 liters water, and then dispersed in 125 ml. water. Half of the preparation was filtered, washed with 800 ml. water and then with ml. acetone, and finally suspended in 60 ml. acetone. In all cases the waterused for washing was distilled. The suspension was used to protect a jet engine lubricant at 450 F., with theresults set forth below in No. 452, Table 1, Example 5. At this tempera ture, the acetone comes out of the mixture. As .is' apparent, by comparison with a control (No. 365), the life of the lubricant was more than doubled, using only: 0.10% by weight of the particles.

The particles described in the preceding paragraph were separated into a fines fraction and a coarser fraction, and the former, having a diameter of about 1 micron and below, were tested as No. 463 of Table 1; they increased lubricant lifetime by 1.6 times. The coarser fraction was tested at a greater concentration, as No. .471 ofTable 1, and increased the lubricant lifetime by 1.9 times.

Example 2 Silver particles were formed by adding dropwise .a solution of 2.6 g. silver nitrate in 250 ml. water to a suspension of 3.27 g. zinc dust in water over a period of 1 hour. After stirring for 3 hours, the resulting silver particles were filtered but now allowed to go dry; they were washed with water, then scraped off in water, filtered, and washed twice with acetone. Then, without letting them dry, the particles were suspended in acetone. They had' a particle size corresponding to a surface area of about 5 sq. m./g'., or about 0.5 micron. Analysis of the particles showed that they comprised 69% silver, with the balance zinc. There was no exposed zinc, as demonstrated by testing with HCl and finding no evolution of hydrogen, so that the particles were actually a mixture of silver particles and particles of silver on zinc. An aliquot portion of the suspended particles were tested according to No. 474, Table 1, and it will be seen that they more than doubled the lifetime of the lubricant. When the particles were dried before use, the increase in lifetime was less but still better than the control.

Example 3 Particles of tin on zinc were prepared by adding fairly rapidly to 6.54 g. zinc dust 10 ml. stannic chloride, using a nitrogen atmosphere to protect against oxidation by air. No heat was evolved. The mixture was refluxed for 2 hours, and then benzene was added to dissolve the excess tin chloride. The mixture was filtered, and the particles, which were not allowed to go 'dry, were washed with benzene. They had a particle size of about 0.5 micron. The particles were used in the oxidation test of No. 566, Table 1, 'where they increased the lubricant lifetime by a factor of about 2.6 times. When used at a lower concen tration, note No. 567, the improvement was less-but still superior over the control.

Example 4 Particles of tin on a core of carbon black were prepared. Carbon particles having a surface area of sq. m./ g. were first mixed for 1.5 hours with a sensitizing agent comprising a solution of 2.5 g. stannous chloride+ 500 ml. water+5 ml. concentrated HCl. They were then filtered on a Milli Pore filter comprising a silver :mem'-' brane having openings of 0.45 micron and washed with 2 liters distilled water. They were next mixed for a suitable time with an activating agent comprising an aqueous solution of 0.1 g. palladium chloride+500 ml. distilled water+0.l ml. concentrated HCl, after which the particles were filtered as before and washed with 2 liters disture of particles of tin on copper, as: prepared in Example 1, and a copper washer, note No. 456; and a mixture of particles of tin on coarse copper, as prepared in Example 1, and a magnesium washer, note No. 470. Table 1 is set forth below.

TABLE 1 Percent Percent Hours to Acid Percent of metal active absorb No. of viscosity Te additive metal 1 mole oxidized increase No. Metal added present in oil 1 O /kg. oil 2 oil at 10 365 None 0 6. 6 565. Aluminum shavings. 0. 900 6. 486 Zinc powder O. 500 6. 5 484. Copper powder (30 0. 500 5. 3 367- Copper washer 6. l 9. l 521 Carbon black 0. 900 7. 3 444 Tin granules (30 mesh) 14.4 7.6 465. Tin on carbon black 0. 900 50 13. 2 452 Tin on copper powder 0.500 0.10 14. 9 456 Tin on copper powder plus Cu 0. 500 0. 15. 9

washer. 463 Tin on copper fines 0.025 0. 0050 10. 5 471- Tin on coarse copper powder 0. 500 0. 10 12. 7 470 'Iin on coarse copper powder plus Mg 0.500 0. 10 11. 3

washer 566 0. 100 0. 0030 17. 0 4. 6 42 567 o 0. 025 0. 0008 7. l 474. i ver powder (Wet 1.50 1.03 15. 4 6.0 37 496. Silver powder (dry). 1. 50 1. 03 8. 6 5. 4 27 49l Lead powder 5 0. 500 0. 500 S. 8 483 Antimony powder 0. 500 0.500

1 This represents the percent of metal under test present, and does not include weight oi supp 2 Samples were oxidized to the extent of 1 level of oxida tion,

ort.

mole of oxygen per kg. of oil. Where the tests were caught at this acid numbers and viscocities were measured.

tilled water. Then they were dispersed in about 100 ml. distilled water and mixed for about 3 hours with one liter of a metal-reducing solution comprising 5 g. copper sulfate+7 g. caustic soda+ g. sodium potassium tartrate+ 1000 ml. water-l-about 10 ml. formaldehyde. Thereafter the particles were filtered and washed with 1 liter distilled water and 1 liter acetone. They comprised copper-coated particles of carbon. About 2 g. of these particles were mixed with 200 ml. of a tin plating solution comprising Shipleys bt27, noted above, and heated to 70 C. for about 2 hours. The particles were filtered on the membrane described, washed with 1.5 liters distilled water, then with 500 ml. isopropanol, and dried in vacuo at room temperature. The product particles now had a coating of tin over the copper. They were employed in test No. 465, Table 1, where they doubled the lifetime of the lubricant.

Example 5 Besides the tests described in the foregoing examples, a number of other agents were tested, as set forth below in Table 1. The test used was the conventional Dornte non-catalytic oxidation test plus measurement of the oxygen absorbed. The test is described in Ind. Eng. Chem. 28 26 (1936). It was carried out in air at 450 F. (232 C.) and comprised heating a sample of lubricant while circulating air through it. The amount of oxygen consumed was measured, as well as the time required for it to be consumed. The same lubricant was used in all tests, including the control (No. 365), and comprised a commercial jet engine oil prepared from pentaerythritol ester base stock; the lubricant contained a conventional amine type antioxidant, i.e., phenyl-alphanaphthyl amine, specifically set forth in Example 1 of US. Patent 3,247,111. The Percent of Metal Additive Present refers to the metal plus any support. Referring to Table 1, the first noted test, No. 365, is the control; then follows tests with aluminum shavings, commercial zinc powder of about 0.5 micron diameter, commercial copper powder of about 300 angstroms diameter, bulk copper in the form of a washer, commercial carbon black of about 250 angstrom units diameter, commercial tin granules of 30 mesh size, lead powder of 0.5 micron size obtained by decomposition of lead tartrate under nitrogen, and commercial antimony powder of about 0.5 micron size. Also tested was a mix- Of significance is the fact that in every case, except No. 521 where carbon black per se was used, the acid number of the oxidized lubricant was less than that of the control. Particularly is this true where tin and silver particles were used, showing that they are able to control the formation of acidic oxidation products. With respect to viscosity increase, in most cases the use of thin and silver particles led to a smaller increase than the control, again showing the ability of the particles to control the formation of undesired products.

The marked improvement in oxidation resistance afforded by the particles of the invention is quite evident. Considering Nos. 465, 452, 456, 463, 471, 470, 566, and 474, where tin and silver particles were used at concentrations of 0.003 to 1.03% by weight, in most cases the lifetime of the lubricant was at least doubled.

Example 6 In another oxidation test, conducted like that described in Example 5 except that the temperature was 585 F. (307 C.), a commercial polyphenyl ether lubricant, containing 5 phenyl rings, was tested without addition of metallic particles, and also in the presence of colloidal copper particles, particles of tin on zinc, and particles of tin on copper. The results are shown in Table 2 below. All particle-containing samples are better than the control, the last providing an increase in lifetime of 2.8 times. The oxidation resistance demonstrated by the control is attributable to the good inherent resistance of this lubricant. In the last two runs the tin content of the particles was on the order of 3%, the balance being either zinc or copper.

Particles of tin on copper on titania were made substantially according to the procedure of Example 4 except that titania of 275 sq. m./ g. surface area. was used instead of carbon black. The particles contained 3.4% by weight of tin, and had a surface area of about 275 sq. m./g., cornumberwas 5.2, andthe viscosity increase was 24%.

By the expression colloidal particles having outer surfaces comprising at least one metal it is intended to include particles composed entirely of one or more metals, and also particles comprising a non metallic core covered by at least one metal layer or shell.

The periodic table classifications as used herein are based on the arrangement distributed by E. H. Sargent & Co. and further identified by the legend Copyright 1962 Dyna-Slide Co.

I It will be understood that the described properties of the metallic particles, as related to their use in lubricants, are applicable to use of the particles in other oxidationsensitive materials.

. In the light of the foregoing description, the following is claimed: I

1. As a composition of matter an organic compound containing, as a protective agent against oxidative deterioration by an oxidizing atmosphere at a temperature of at least 400 F., at least 0.005 percent by Weight of colloidal particles comprising a substrate having a surface coating ofa'metal selected from the group consisting of tin, silver, antimony, lead, bismuth, and palladium.

2. The composition of claim 1 wherein said organic compound is a lubricant.

3. The composition of claim 1 wherein said metal is tin. 4. The composition of claim 1 wherein said metal is silver.

I 5. The lubricant of claim 2 comprising a major proportion of an ester formed by reaction of a pentaerythritol 5 and an organic acid having 2 to 18 carbon atoms.

6. The lubricant of claim 2 in which there is also present,

(a) about 0.5 to 5% of a conventional antioxidant, (b) about 0.0001 to 1% of an equimolecular salt of 1- salicylalaminoguanidine and an aliphatic carboxylic acid having 14 to 18 carbons, (c) about 0.001 to 1% of a polyhydroxy-anthraquinone,

(d) about 1 to 10% of a phosphorus compound chosen from nuetralorganic'phosphates and phosphit'es,

(e)' and 0.0001 to'0.01% of'afconventional defoam'ant; all percentages being by weight based 'oh'the' lubri cant.

7. The lubricant of. claim 2 wherein said metal is tin, present in an amount less than about 5% by weight.

8. The lubricant of claim 2 wherein said metal is silver, present in an amount less than about 5% by weight.

9. As a composition of matter, an organic lubricant comprising a major proportion of an ester formed by reaction of a pentaerythritol and an organic acid having 2 to 18 carbon atoms containing, as a protective agent against oxidative' deterioration by an oxidizing atmosphere at a temperature of at least 400 F., at least 0.005

percent by weight of colloidal particles comprising a substrate having a surface, coating of a metal selected from the group consisting of tin and silver.

10. The composition of claim 9 wherein said substrate 15 zinc.

11. The composition of claim 9 wherein said substrate is copper and said metal is tin.

12. The composition of claim 9 wherein said substrate is carbon black and said metal is tin.

References Cited UNITED STATES PATENTS 2,160,911 6/1939 Russell 252-26 X 2,321,203 6/ 1943 Henry 252.-26 2,334,738 11/1943 Wultf 252---26 v 2,742,427 4/1956 1 Reitf 2521 9 2,970,927 2/1961 David 252- 26 X 3,180,835 4/1965 Peri a 25226 X, 3,247,111 4/ 1966 Oberright et al. 252 X 3,267,032 8/1966 Ravner 252-26 DANIEL E. WYMAN, Primary Examiner WILLIAM J. SHINE, Assistant Examiner US. 01. X.R.

2 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,507,789 Dated Ap 97 Inventor(s) Israel J. HeilWeil and Albert L. Williams It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 65, "indequate" should read --inadequate-- Column 2, line 12, "hydroxyanthaquinone" should read --hydroxyanthraquinone-- Column 4, line 70, "Carbon particles" should read --Carbon black particles-.

Column 6, line 38, "thin" should read --tin--.

Column 8, line 2, "nuetral" should read -neutral--.

AUG 251370 (SEAL) Attest:

WILLIAM rmmm Edward M. Flam!!- Owmisliomr or Pat-outs Attesting Offim 

